Current limiting fuse



June 15, 1965 s. R. SMITH, JR

CURRENT LIMITING FUSE Filed July 28, 1961 IIIIIIIIIIII l United States Patent O 3,139,7ll CURRENT LIMHTING FUSE Sidney R. Smith, Jr., Stockbridge, Mass., assigner to Gen eral Electric Company, a corporation of New York Filed July 28, 1961, Ser. No. 127,608 4 Claims. (Cl. 26d-126) This invention relates to an electrical circuit protective device, and more particularly to an electrical circuit protective device which is generally referred to as a current limiting fuse.

Current limiting fuses are presently well known in the circuit protective field, and enjoy a relatively extensive use therein. As is well known to those skilled in this art, current limiting fuses generally comprise one or more conductors of a suitable fusible material, such conductors being enclosed or embedded in an inert granular material, such as for example, sand, quartz, or similar arc-extinguishing material of high dielectric strength. The conductors and the granular material are enclosed in an outer casing which is generally provided with end caps to form the terminals of the current limiting fuse. When these fuses are subjected to high current, due to various faults in the circuits they are designed to protect, the conductor or conductors fuse or melt and an arc is drawn which is rapidly dissipated by the granular material. This arc dissipation is accomplished by the transfer of heat from the arc to the relatively cool granular material. The current limiting effect is obtained by the effective large resistance which is placed in the current path, due to the melting of the fusible conductor or conductors and to the high arc resistance which results from the heat dissipation mentioned above.

As will be understood, the rating of a current limiting fuse is generally determined by the size and length of the various fusible conductors which are used therein. In order to increase the voltage rating of such fuses, without substantially increasing their length, it has been the practice to Wrap the fusible conductors about an insulated core body, such as is shown in Patent No. 2,188,816. This also provides for a longer arc path when the fusible Wire melts, as well as providing for greater contact between the arc and the inert granular material to more rapidly quench the arc formed. It has been proposed, in the prior art, to merely wind the exible wire in a helical fashion and insert it into the enclosure of the current limiting fuse without the aid of a core piece. This is shown, for example, in Patent No. 2,337,937. This of course greatly simplifies the construction of such current limiting fuses, as is pointed out in the above-mentioned patent. However, where a number of fusible conductors are used to make a Current limiting fuse, much care is required in the manufacture of such fuse and in the placing of the various conductors so as to prevent the various arcs, which may form at the fusing of the different conductors, from merging. As will be understood, the merging of these arcs will substantially eliminate the current limiting benefits of the fuse. To aid in this separation of the various arcs, care is required in packing the granular material in the enclosure which forms the exterior part of the current limiting fuse. One method of packing such granular material is disclosed in Patent No. 2,337,937.

Further, even when the wires are properly spaced during manufacture, the various fusible wires may tend to drift together during use of such current limiting fuses. This drifting is generally the result of vibration, to which such fuses may be subjected during use. Also, it has been found, that even when such fuses have their various fuse wires properly spaced and care is used in filling such fuses with a dielectric such as sand, failures have occurred. These failures have in general been considered to occur from failure of the dielectric to be retained in its completely filled position, due to subsequent shifting of such material. Another cause of such failure is due to the momentary pressure of the arc gasses during fusing. These gases may cause a crevice to form in the sand, providing communication between the various fuse wires. This communication allows the various arcs to channel down a single path.

From the 1above `it lwill be apparent to those skilled in the art that there is presently a need in the current limiting fuse field for a fuse which would be relatively simple to manufacture with a plurality of fusible conductors therein, which will positively prevent the merging of the arcs on blowing of such fuse, and which will enable a variety of fuse ratings to be provided without changing the outer casing, which encloses the current limiting fuse. Further, as is well known, a current limiting fuse being substantially sealed with the granular material therein, it is relatively impossible to tell when a fuse has blown without the benefits of some kind of signal or indicating device to indicate the condition of the tube. Clearly, it is desired in the current limiting fuse to provide such indicator means so that it will be possible to tell at a glance the operating condition of the current limiting fuse.

It is therefore one object of this invention to provide a new and improved current limiting fuse.

It is a further object of this invention to provide a current limiting fuse which has a plurality of fusible conductors therein and to maintain the arcs which are formed by fusing of such conductors entirely separate from each other.

A further object of this invention is to provide an improved current limiting fuse having a plurality of fusible conductors therein which is relatively simple to manufacture.

Still another object of this invention is to provide a current limiting fuse having a plurality of conductors where the rating of such fuse can be varied without changing the exterior of the current limiting fuse.

A still further object of this invention is to provide an improved current limiting fuse utilizing a plurality of fusible conductors therein with a simple, inexpensive means to indicate the operating condition of such current limiting fuse.

In carrying out this invention in one form, a current limiting fuse is provided which comprises an enclosure member of ceramic or other insulating material. The enclosure member is formed from a solid piece of insulating material and is provided with a plurality of tubular channels or compartments extendmg therethrough. A plurality of fusible conductors are provided, one being placed in each of said compartments, and end caps are provided making electrical Contact with the conductors and sealing the ends of the enclosure. A granular material is placed in each compartment about the conductors therein prior to sealing one of the end caps. The fusible conductors may be coiled, as desired, in each compartment to provide any desired fuse rating.

When indicating means are desired, an opening is provided in one of said end caps, the opening being closed by an indicating means. The indicating means is surrounded by a spring which tends to force the indicating means out of said opening; the indicating means being secured to the opening by means of a fusible wire through the body of the current limiting fuse. The fusible wire is so designed, as to size and material, that it will be the last fusible conductor to melt, thereby releasing the indicating device to provide an indication that the fuse has blown.

The invention which it is desired to protect will be clearly pointed out and distinctly claimed in the claims appended hereto. However, the details of this invention, and manner in which its objects and advantages are obtained, as Well as other objects and advantages thereof, will be better understood from the following detailed description of a preferred embodiment thereof, when taken in connection with the accompanying drawing, in which:

FIGURE l is a sectional plan view of a current limiting fuse made according to one form of this invention;

FlGURE 2 is a sectional view taken on the lines 2-2 of FGURE l;

FiGURE 3 is a sectional plan View of a current limiting fuse similar to FlGUllE l, showing the use of an indicating means therewith; and

FlGURE 4 shows an open-type cut-outl showing one manner in which the currentlimiting fuse of FlGURE 3 may be used.

Referring now to the drawings, in which like numerals are used to indicate like parts throughout, and with particular reference to FGURE l, there is shown a current limiting fuse itl which comprises a body of insulating material l2, the body being provided with a plurality of tubular channels or compartments 14 extending completely therethrough with a fusible conductor member 1 placed in each of the compartments 14. End caps i8 and 2li are provided sealing each end of the insulated body, and a granular material such as, for example, sand, is provided in each of the compartments 14 surrounding the fusible conductor llo. The granular material is indicated in the rawings by the number 22. As can be seen, by means of this fuse, each of the fusible conductors are separated into separate compartments, and therefore there is no opportunity for the various arcs, which are drawn when the fuse wires melt, to merge during fuse interruption. The separate cham ers also present fewer problems in the'filling of the different compartments with the granular material, inasmuch as it is not necessary to rely upon the placing of the fuse wires or the granular material to provide the separation of the arcs. As is clearly indicated in FlGURE l, the various fusible conductors may be coiled as desired, to thereby provide for a dilerent type of fuse rating as desired, without lengthening in any manner the exterior casing l2 of the current limiting fuse. Of course, it will be understood, that the voltage rating of the fuse depends primarily on the length or the fuse wire. By ceiling such fuse wire a greater length of wire may be obtained without increasing the overall length of the fuse body.

Considering FIGURE l now in more detail, the insulated body l2 may be made of insulating material such as a ceramic material. As is well understood, it may be extruded from such material with the openings or chambers 14 therein. Extruding is obviously preferred since it is relatively inexpensive, thereby reducing the manufacturing expense of the fuse. At the ends of the ceramic or insulated body l2 there are provided cushion disks 24 which may be for example, an asbestos cloth or other insulating material. Gn the exterior of the cushion disks 214, metallie disks 26 are provided. As can be seen from FIG- URE l, the fusible conductors t6 are strung through the chambers i4, through openings in the cushion disk 24 and the metallic disk 26, and, as indicated at 28, they are twisted together at the top of the metallic disk 26 and, if desired, may be soldered to such disk.

Of course, as will be understood, in the general manufacture of the current limiting fuse, the bottom cushion 24 and the bottom disk 26 and the bottom end cap Ztl would be placed in position, and the fusible conductors le would be drawn through tne upper cushion disk and metal disk 24 and 26, respectively. Before these disks 24 and 26 were placed on top of the ceramic, or insulating body l2, the sand, or other granular liller material, 22 would be placed in the chambers 114. When the chambers M were lille-d then the cushion disk 24 and metal cap 26 would be placed firmly thereagainst and the upper portions of the conductor wire would then be twisted and laid against the upper metal disk 2d. As before mentioned, if desired, the upper portions of the conductors could be attached to the metal disk vsuch as, for example, by soldering. However, as will be understood, when the metal end cap 1S is placed over the top of the insulated body l2 it is pushed firmly against the wires 2.8, thereby making a drm connection between the wires 2.3, the metal end cap i8, and the metal disk 26. As will be seen from FIGURE l, the metal end cap i8 is cemented to the insulated body l2, by any desired manner, to provide an adequate seal between the end cap and the insulating material. Of course, in a similar manner the bottom end cap 2li is also sealed to the insulating body l2. j

lf desired, the current limiting fuse of this invention may be provided with an indicating means in order to show when the current limiting fuse has operated. Such current indicating means is shown in FIGURE 3 as attached to the lower end cap 20a. As indicated in FIG- URE 3, an opening 30 is provided in the metal end cap 26u and in the metal disk 26a, such opening being closed by means of the indicator means 32. A boss 34 is formed on the metal end cap 2da about the opening 3@ and a lip 3S of the indicator means 32 butts thereagainst when the indicating means is in place, as shown in FIG- URE 3. A compression spring, indicated at 36, is provided about the outside of the boss 34 and is compressed between the metal end cap Ztl and the lip 3S formed on the indicator means 32. An indicator Wire 49 is irmlyV attached to the indicator means 32, at one end thereof, the opposite end extending through a compartment 14 and into the upper metallic disk 26 as indicated. The indicator wire 4@ is so designed, as to thickness of wire and material, such that it will not melt until the other wires have been fused. Therefore, the entire current is across the wire 4u. The wire 4t) will then melt, which will release the indicating means 32 which will then be pushed out of opening 3l) by means of the expansion of compression spring 36. As indicated in FIGURE 3 in order to provide `an adequate seal between the indicating means 32 and the interior of the chamber 14, the O-ring seal 42 is provided. Thus it can be seen that by means of a change in the design of the base or lower end cap member 2da, an indicator means may be provided to indicate the operation of the current limiting fuse of this invention, if desired.

Referring now to FIGURE 2 of the drawing, it can be seen that the ceramic or insulating body 12 is provided with a plurailty of compartments or channels 14 therethrough. As shown in FlGURE 2, seven compartments are provided, but it will be understood that the number of compartments will be provided according to the desired rating of the current limiting fuse. Obviously, if it is desired to have a heavier rated fuse more openings or compartments 14 could be provided, Whereas if the rating ofthe fuse is to be of relatively lower value a lesser number of channels or compartments 14 may be provided. Of course, it will be understood that, while the openings 14 are shown as being tubular or circular in cross section, they may be of any other shape as desired.

However, it has been found that by means of extrusion of the insulated body 12 it is simpler to extrude tubular chambers l/.l than any other shape.

Referring now to FGURE 4 of the drawing, there is shown an open cutout which may utilize the current limiting fuse of this invention. Considering FIGURE 4 of the drawing, the open cutout is provided with an upper terminal 44 and a lower terminal 46, which may, of course, be connected to the conventional open cutout contacts, as is well understood by those skilled in the art. As shown, the upper terminal 44 may be provided with a ring member 48 which may be engaged by a hotstick (not shown) to open or close the cutout as desired. Between the terminals 44 and 46 is placed the current limiting fuse lll of this invention. As will be understood, the end cap 18 is surrounded by the upper terminal 44, and, by means of the bolt 50, the upper terminal is securely fastened to the upper metal end cap 18, thereby making lirm electrical contact therewith. In a similar manner, the lower terminal 46 is securely fastened to the lower metal end cap by means of the bolt S2, so .as to firmly secure the terminal 46 to the current limiting fuse 10 and make a rm electrical connection between the end cap 20 and the terminal 46.

Inasmuch as the Icurrent limiting fuse of this invention is not of the expulsion type, it is desirable to make use of the indicating means 32 to provide a means for opening the cutout member should the fuse 10 be operated. As can be seen from FIGURE 4, the indicator means 32 is provided with a slot between the end cap 54 and the lip 38 into which is inserted a dropout lever means 56, which forms part of the lower contact 58 of the cutout. As will be understood when the fuse opens and the indicator means 32 is released, the lever 56 will pull down due to spring pressure, thereby releasing the upper terminal 44 of the cutout to thereby enable the cutout to dropout and rotate about the trunnion member 60. Thus it will be clear that, by means of the current limiting fuse of this invention, the fuse may be utilized in an open cutout to perform the desired current limiting function and, at the same time, to allow the cutout to operate in its normal manner when the fuse member has operated.

Of course it will be understood by those skilled in the art that the current limiting fuse of this invention may be utilized in any of a number of areas where the normal fuse is utilized, as well as being utilized in those areas where a current limiting fuse is desired. There has been shown and described the use of the current limiting fuse of this invention with an open cutout but of course, it will be understood, that the invention is not to be limited thereby, since it will clearly appear to those skilled in this art that the current limiting fuse of this invention may be utilized in any other manner as a normal tubular fuse is used.

While there has been shown and described the present preferred embodiment of this invention, it will be understood by those skilled in the art that various changes may be made in the details of construction and the materials utilized in the invention. Therefore, this invention is not to be considered as limited to the details of construcl tion herein set forth but all changes in construction and materials are considered to be part of this invention, as will fall within the spirit and scope of the appended claims.

What is claimed as new and which it is desired to be secured by Letters Patent of the United States is:

1. A current limiting fuse comprising a fuse body of insulating material, said body being provided with a plurality of parallel channels extending therethrough, a plurality of fuse wires, each of said fuse wires being threaded through a separate one of said parallel channels, each of said channels being lled with a granular inert material, metal end caps secured to opposite ends of said body and being in electrical contact with said fuse wires, cushion disks provided at opposite ends of said fuse body between said body and said metal end caps, said cushion disks serving to retain said granular material in said chambers, indicating means provided in one of said end caps, said indicating means being spring biased to an indicating position and being held in a non-indicating position by one of said fuse wires, said one fuse wire being designed as to size and material that it is the last fuse wire to melt on operation of said current limiting fuse.

2. A current limiting fuse comprising a fuse body of insulating material, said body being provided with a plurality of parallel channels extending therethrough, a plurality of fuse wires, each of said fuse wires being threaded through a separate one of said parallel channels, each of said channels being filled with a granular inert material, metal end caps secured to opposite ends of said body and being in electrical contact with said fuse wires, indicating means provided in one of said end caps, said ndicating means being spring biased to an indicating position and being held in a non-indicating position by one of said fuse wires, said one fuse wire being designed as to size and material that it is the last fuse wire to melt on operation of said current limiting fuse, said one fuse wire being a substantially straight wire, the remainder of said fuse wires being coiled within said parallel channels.

3. A current limiting fuse comprising a fuse body of insulating material, said body being provided with a plurality of parallel channels extending therethrough, a plurality of fuse wires, each of said fuse wires being threaded through a separate one of said parallel channels, each of said channels being filled with a granular inert material, metal end caps secured to opposite ends of said body and being in electrical contact with said fuse wires, indicating means provided in one of said end caps, said indicating means being spring biased to an indicating position and being held in a non-indicating position by one of said fuse wires, said one fuse wire being designed as to size and material that it is the last fuse wire to melt on operation of said current limiting fuse, said fuse being mounted in a dropout open cutout, said indicating means being connected to a dropout lever in the lower contact of said cutout, whereby when said fuse operates said dropout lever will function to open said cutout.

4. A current limiting fuse comprising an extmded fuse body, a plurality of parallel compartments formed in said body and extending therethrough, cushion disks mounted on opposite ends of said body, metal disks mounted on opposite ends of said body holding said cushion disks against said body, openings in said cushion disks and said metal disks, said openings being aligned with said compartments, a plurality of fusible wires, each of said fusible wires being threaded through one of said compartments and through said disks, opposite ends of said fusible wires being connected together eXteriorly of said metal disks, metal end caps for said fuse body, said end caps being secured to opposite ends of said body and providing electrical contact with said connected opposite ends of said fusible wires, an inert granular material lling each of said compartments, said cushion disks serving to retain said inert granular material in each of said compartments.

References Cited by the Examiner UNITED STATES PATENTS 2,156,058 4/ 39 Lohausen 20G-120 2,180,874 11/39 Hunter et al. 200-120 2,216,661 10/ 40 Dannenberg 200-120 2,343,224 2/44 Powell 20G-121 2,343,422 3/ 44 Rawlins 200-120 2,421,658 6/ 47 Strang et al. 200-121 2,439,674 4/ 48 Schuck 200--120 2,605,371 7/ 52 Fannoe 200-121 2,794,095 5/57 Kozacka 200--120 FOREIGN PATENTS 3,883 2/ 10 Great Britain.

480,044 2/ 38 Great Britain.

508,959 7/ 39 Great Britain.

120,993 2/ 46 Australia.

812,058 4/ 37 France.

BERNARD A. GILHEANY, Primary Examiner. 

4. A CURRENT LIMITING FUSE COMPRISING AN EXTRUDED FUSE BODY, A PLURALITY OF PARALLEL COMPARTMENTS FORMED IN SAID BODY AND EXTENDING THERETHROUGH, CUSHION DISKS MOUNTED ON OPPOSITE ENDS OF SAID BODY, METAL DISKS MOUNTED ON OPPOSITE ENDS OF SAID BODY HOLDING SAID CUSHION DISKS AGAINST SAID BODY, OPENINGS IN AID CUSHION DISKS AND SAID METAL DISKS, SAID OPENINGS BEING ALIGNED WITH SAID COMPARTMENTS, A PLURALITY OF FUSIBLE WIRES, EACH OF SAID FUSIBLE WIRES BEING THREADED THROUGH ONE OF SAID COMPARTMENTS AND THROUGH SAID DISKS, OPPOSITE ENDS OF SAID FUSIBLE WIRES BEING CONNECTED TOGETHER EXTERIORLY OF SAID METAL DISKS, METAL END CAPS FOR SAID FUSE BODY, SAID END CAPS BEING SECURED TO OPPOSITE ENDS OF SAID BODY AND PROVIDING ELECTRICAL CONTACT WITH SAID CONNECTED OPPOSITE ENDS OF SAID FUSIBLE WIRES, AN INERT GRANULAR MATERIAL FILLING EACH OF SAID COMPARTMENTS, SAID CUSHION DISKS SERVING TO RETAIN SAID INERT GRANULAR MATERIAL IN EACH OF SAID COMPARTMENTS. 